We propose to continue our investigation of the properties, modes of action, and regulation of the three E. coli elongation factors, EF-Tu, EF-Ts and EFG, which function with the guanine nucleotide and the ribosome to effect protein chain growth. We will also isolate and investigate the comparable factors present in eukaryotic cytoplasm and mitochondria. We will examine the following conceptually and operationally related issues as they relate to these proteins and the reactions in which they participate: 1) Definition of factor active sites through selective chemical modification. 2) Substrate specificity and the mechanism of GTP hydrolysis by factors. 3) Metal ion involvement in factor function. 4) Location of interactions between the factors and the ribosome. 5) Mapping of interactions between EF-Tu and amino acyl-tRNAs. 6) Examine the regulation of factor function. 7) Isolation and comparative features of eukaryotic cytoplasmic factors. 8) Isolation and comparative features of eukaryotic mitochondrial factors.